In fluid mechanics, it is known that the efficiency of sails made of fabric is less than that of the wings of aircraft. In the latter, the difference between the lift force and the weight enables the aircraft to fly, due to the aerodynamic boundary layer of the air not being separated from the profile. Conversely, in conventional sails in the naval sector, it is the thrust of the wind that fills the sail and produces, by means of its thrust, a resulting force which enables the forward movement of the boat or ship.
It has been desired for many years to achieve a sail for aquatic navigation that presents the advantages of an aircraft wing. To this end, there have been numerous attempts to achieve rigid sails with an aerodynamic profile of an aeronautical nature.
Among these, the Flettner-type rotors are worthy of mention; these were described in 1926 by Anton Flettner (FLETTNER, Anton Mein Weg zum Rotor, Leipzig (Köhler & Amelang, 1926)), quoted previously, for example, in the European patent document EP 040 597.
Document WO2004024556 describes a rigid sail comprised of two parts that may rotate around a vertical shaft to determine the intrados and extrados of a sail by way of an aerodynamic profile of the kind used for wings in aeronautical technology.
Document WO0189923 describes a rigid sail with an articulated aerodynamic profile comprised of three vertical elements (or modules), each of which is formed by three horizontal elements (or sections), mutually articulated or extrados of the wing or rigid sail.
Patent FR2648426 describes a wing comprised of a rigid part and a flexible part which is retracted into the interior of a housing in the rigid part, enabling different aerodynamic configurations.
U.S. Pat. No. 7,146,918 describes a system for the generation of electrical energy and hydrogen from seawater and wind energy in systems floating in the water and which comprise rigid sails.
The problem entailed in the generation system of U.S. Pat. No. 7,146,918 is that the operation, control and regulation of the sails is complex, with the consequent loss of performance and predictability in the production of power and H2. For example, a significant problem is that should the wind change direction by 180°, it becomes necessary to perform the operation of turning the sails, which may be complex and hazardous.
Notwithstanding this profusion of attempts, of which only a number of illustrative examples have been listed, a device that is versatile, economical and simple to operate has to date not yet been achieved.
Document EP2202144A1 describes a rigid sail having a configurable profile, with elastic enclosing sheets, joined to the corresponding wall in at least one zone near the furthest edge and a means for the generation and supply of air under pressure and of a vacuum in order to inflate and deflate the sails to modify the profile of the sail as desired. This sail provides a solution to this requirement.
U.S. Pat. No. 8,601,966 describes sails with an aerodynamic profile, foldable and unfoldable as in the style of an accordion bellows, and which provide an effective, high-performance solution for the production of hydrogen and other chemical species with a high enthalpic content. The sails form an array formed by opposing pairs of sails, each of which comprises a number of extendable masts, a number of sections longitudinally displaceable along said masts and a number of panels, articulatedly joined to the sections and to each other, forming the lateral surface of each sail. Said panels are operative between two positions: an unfurled operative position, wherein they are essentially coplanar and longitudinally aligned in an essentially vertical direction; and a furled stowing position, wherein they are stacked as in the manner of a bellows, jointly with the sections in an essentially horizontal position.
Notwithstanding the efficiency and versatility of the sail of U.S. Pat. No. 8,601,966, the method of furling might present drawbacks of a mechanical and operative nature, when it might be attempted to furl or unfurl rapidly, for example due to a change in the climatic conditions.
One of the objectives of the present invention is to provide a simultaneous solution to the aforementioned problems and drawbacks.